In the field of infrared imaging, the current objectives are to provide technology for large area focal plane arrays for long wave infrared radiation (LWIR), multispectral applications, and to provide this technology at low cost with high performance. Substantial performance has been shown by second generation photovoltaic (PV) mercury cadmium telluride (MCT) diode technology. Although MCT technology has desirable performance, it has substantial drawbacks in terms of manufacturability and uniformity. A newer, high impedance photoconductive (PC) detector technology for infrared detection termed quantum well infrared photodetector (QWIP), is based on the Gallium Arsenide (GaAs)/Aluminum Gallium Arsenide (AlGaAs) material system. This technology has significant producability and uniformity advantages over second generation PV MCT technology. This is primarily because it is based on mature GaAs/AlGaAs material and processing technology. However, QWIP technology suffers from a performance disadvantage in comparison to second generation PV MCT technology. A primary performance problem with QWIP technology is the requirement for a substantially higher bias voltage for operation which results in the production of a large dark current. The large dark current lowers the sensitivity (D.sup.*) of the detector. The excessively large dark current also severely limits the sensitivity of the detector when used within a focal plane array (FPA). Another performance problem with QWIP technology is reduced quantum efficiency relative to PV MCT technology.
In view of the desirable manufacturing qualities of QWIP, there exists a need to improve the performance characteristics of QWIP infrared detectors in the efficiency of the collection of infrared energy and in the reduction of signal noise and for improved tuning of such detectors. The present invention has the advantages of increased signal output and decreased noise.